The epoxytriazole derivative represented by the formula (VI) (hereinafter to be also referred to as epoxytriazole derivative (VI)) is a useful synthetic intermediate for anti-fungal agents, such as triazole compounds described in JP-A-4-356471, U.S. Pat. No. 5,405,861 and the like.
The production methods of epoxytriazole derivative (VI) have been reported in, for example, Bulletin of the Chemical Society of Japan (Bull. Chem. Soc. Jpn), Vol. 67, 1427-1433 (1994), The Chemical Society of Japan, May 1994, vol. 67, No. 5, pp. 1427-1433, Chemical & Pharmaceutical Bulletin (Chem. Pharm. Bull.), Vol. 43(3), 432-440 (1995), Pharmaceutical Society of Japan, vol. 43, No. 3, pp. 432-440 (1995) and the like. According to these methods, as shown in the following reaction schemes, epoxidation of a compound of the formula (VII) (hereinafter to be also referred to as compound (VII)) wherein hydroxyl group is protected by a protecting group, such as tetrahydropyranyl group and the like, is conducted using trimethyloxosulfonium halide. 
The compound (VII) used as a starting material in conventional methods can be produced by protecting hydroxyl group of a compound, wherein tetrahydropyranyl group of the formula (VII) has been substituted by hydroxyl group (to be also referred to as a deprotected compound of compound (VII)), with tetrahydropyranyl group. However, the introduction of a protecting group is uneconomical because it requires an equimolar amount of tetrahydropyranyl derivative relative to the deprotected compound of compound (VII), and the like. In addition, the introduction of protecting group necessitates a deprotection step, thus increasing the number of steps and the like. Moreover, the introduction of protecting group leads to inefficiency. Thus, this method is industrially disadvantageous. According to conventional methods, moreover, stereoisomers, which are in a diastereomeric relationship and resist use thereof as an intermediate for a triazole compound, which is an anti-fungal agent, are by-produced in about 20%. The α-hydroxy-ketone derivative, which is a deprotected compound of compound (VII), is chemically unstable, and the above-mentioned epoxidation without protection of hydroxyl group has been considered to be difficult.
It is therefore an object of the present invention to provide a method for economically and efficiently producing epoxytriazole derivative (V) to be mentioned below, such as epoxytriazole derivative (VI) and the like, or an intermediate therefor, with high quality by an industrial means.